This invention is related to smoke detectors. In particular, it is a device to prevent the insertion of a battery door in a smoke detector unless the battery door is equipped with a battery.
Smoke detectors have become accepted as primary means of warning for people in living spaces that are threatened by fire. Battery-powered smoke detectors are of particular utility in providing protection for residential spaces, mobile homes, motor homes, and hotel and motel rooms. Electrical codes are increasingly being amended to require smoke detectors in such locations.
The warning offered by a battery-powered smoke detector, however, is illusory if the smoke detector lacks a battery. Perhaps the most likely reason for a smoke detector to lack a battery is removal of the battery to prevent the smoke detector from sounding its alarm in a location near a kitchen, where the smoke detector may be affected by smoke or other combustion products from cooking. Occasional smoke from a fireplace may trigger a smoke detector that is located near the fireplace. Sometimes a smoke detector may be triggered by high humidity. All too often the reaction of a householder to a smoke detector that sounds an alarm in response to one of the conditions described above is to remove the battery to silence the detector. If the detector is then put back into apparent operating condition without the battery, it is no longer capable of giving a warning in case of a real fire.
One solution to the problem of smoke detectors that provide alarm signals in response to burning toast or smoky fireplaces is given in U.S. Pat. application Ser. No. 892,668 and U.S. Pat. No. Design 297,316, both of which are incorporated by reference as if set forth fully here. The smoke detector in the '668 application includes a silence feature, which reduces the sensitivity of the detector for a period of a few minutes after the detector is activated so as to give the unwanted smoke time to clear. In the smoke detector of the '668 application, the smoke detector continues to be functional with a sensitivity that is reduced initially and that increases over a period of four to ten minutes until the original sensitivity is restored. If the smoke condition continues when the sensitivity of the detector returns to a level at which the detector will sound an alarm, the patience of the householder may be stretched to the point of causing battery removal to stop the noise once and for all.
Another reason for battery removal occurs when people see the smoke detector as a source of a battery that they need for another appliance. Such perceived needs have led to the removal of batteries from many smoke detectors, rendering them inoperative when they are needed.
The threat of battery removal has led to the issuance of a standard by Underwriters'Laboratories to provide either a warning or a preventive. The warning would display a flag or a sign so that an observer could tell that a battery had been removed from the detector. The preventive would interfere with closure or reassembly of the smoke detector if the battery had been removed.
Most battery-powered smoke detectors require some disassembly of the detector to get at the battery for changing. In contrast, the smoke detector of U.S. Pat. application Ser. No. 892,668 includes a removable battery door into which a battery is snapped. Contacts from the battery terminals are connected to terminals in the smoke detector to supply battery power to operate the detector. However, in the invention as disclosed in the '668 Application, there is no way to tell from the outside of the detector whether or not a battery is installed in the removable door.